Scintillation scanner photo-circuit



Dec. 1, 1964 J. B. STICKNEY ETAL SCINTILLATION SCANNER PHOTO-CIRCUIT 2Sheets-Sheet 2 Original Filed June 15, 1959 RATE METER INVENTORS JOSEPHa. STICKNEY, WALTER E. SPLAIN 6 BY CARL E. HERRING ATTORNEYS 3,159,744SCINTHLLATMEN SCANNER PHOTO-CIRCUIT Joseph it. Sticliuey, Rocky River,(thin, Carl E. Herring, Ann Arbor, Mich, and Walter E. Splain, FairviewPark, Ohio, assignors to Picker X-Ray Corporation, Waite ManufacturingDivision, Inc, Cleveland, Ohio, a corporation of Ghio Continuation ofapplication Ser. No. 820,503, June 15, 1959. This application Feb. 6,1963, Ser. No. 257,373 29 Claims. (Cl. 250-415) This is a continuationof application Serial No. 820,5 ()8 filed June 15, 1959.

This invention relates to scintillation scanning devices and moreparticularlyto a photorecording system for producing a graphicpresentation ofthe distribution and concentration of radioactivity in anarea.

In a copending application for United States patent entitledScintillation Scanner, filed. by Joseph B. Stickney, Clarence E.Le'rnmermann, Carl E. Herring, and Roland W. Carlson, filed June 1,1959, and bearing the Serial Number 817,403, new U.S. Patent No.3,070,695, which issued on December 25, 1962, a mechanism for conductinga scintillation study is disclosed. In that mechanism a scintillationprobe is supported on a boom which reciprocates along a series ofparallel rectilinear paths to cover a predetermined area. A light sourceand a stylus are also carried by the boom to reciprocate along pathsoftravel which parallel the probe path of travel. The light source. andthe stylus are electrically connected to the probe to simultaneouslyproduce graphic images, on both a film and a sheet or paper, or theactivity being measured.

' The present invention 'is directed to the use of a cathode ray tube asa light source and a novel and improved system for transmitting impulsesfrom the scintillation probe to the tube and emitting light pulses fromthe tube which are proportional in both firequency and brightness to therate of activity detected by the probe.

With the present inventiona discriminating type amplitier is connectedto the scintillation probe. The armplifier is of the type which willemit impulses only when pulses within a preselected range of amplitudeare fed into it. If a scintillation crystal such as thallium-activatedsodium iodide is used in the probe, the pulses produced by the probe areproportional in amplitude to the quantum energy absorbed by the crystal.The discriminating amplifier selects pulses corresponding to a givenrange of quantum energies, while rejecting all other pulses.

A one-shot multivibrator is connected to the discrimh nating amplifier.The multivibrator emits one pulse of a predetermined time duration foreach impulse received from the discriminating amplifier. The pulsesemitted by the multivibrator are transmitted to the cathode of a cathoderay tube. With this construction, the cathode will emit one impulse foreach count detected by the probe and passed by the amplifier.

A rate meter (or pulse frequency meter) and a variable amplifier areseries connected to the discriminating amplifier. The rate meter andvariable amplifier are each adjustable to provide appropriate outputimpulses which vary with the activity being studied. The variableamplifier controls a variable voltage power supply within apredetermined range. The power supply is connected to the acceleratorelect-rode of the cathode ray tube.

1 Since the output of the rate meter and the variable amplifier isproportional to the rate of radiation quantum nited States Patent3,159,744 Patented cc. 1, 1964 Accordingly,,one of the principal objectsof this inven tion is to provide a novel and improved photorecordingsystem responsiveto radioactivity, which system has a light output whichvaries with the rate of activity detection.

A related object of the invention is to provide such a system in whichthe light pulse output varies both in frequency and intensity with thecount rate.

Expressed another way, a principal object of the invention is to providea novel and improved photorecording system in which the density of aproduced photographic image may be proportional to a detected countrate, or in which the contrast of the image may be artificiallyenhanced.

As an example of the foregoing object, it is possible to so adjust thedisclosed device that any selected minimum count rate will produceminimal density on the film, andsimultaneously any selected maximumcount .rate will produce maximum useable density.

In prior proposals for some recording systems respon-' Sive to ameasurement of radioactivity, it is common to record only a selectednumber of the counts, which selected number is often a power of two. Forexample, every other, or every fourth, or every eighth count may bemeasured. With the system of this invention all counts aremeasured solong as a selected minimalactivity is exceeded.

Accordingly, another object of this invention is to provide a novel andimproved photorecording system in which the image produced reflect-seach and every impulse emitted by the probe in response to detectedactivity,

Still another object of the invention is to provide a novel and improvedphotorecording system in'which there is no time delay provided in thesystem so that the cathode ray tube emits a light pulse substantiallyinstantaneously after the probe detects a measurable radioactive andclaims, taken in conjunction with the accompanying drawing, in which:

FIGURE '1 is a schematic view of'the novel and improved photorecordingsystem; and,

FIGURE 2 is a wiring diagram of the variable gain amplifier and thepower supply. i

Referring to the drawing, a scintillation probe is shown generally at10. The probe 10 may take anyfof the usual and well lmown forms.- Theseusual forms normally. comprise a fluorescent crystal, a photoelectrictube, suite able circuitry to energize the tube and to transmit outputimpulses from the tube, and suitable heavy metal shielding andcollirnatingmeans to render the probe sensitive to radiation fromessentially only one direction. The output impulses are transmittedthrough a conductor 11 to i V a suitable discriminating amplifier 12.

detection by thepro-be, the voltage of the accelerator electrode is alsoproportional to the rate of detection or the count rate. For this reasonthe intensity of each dash of light emitted by the cathode ray tube willbe proportional to the count rate.

- The discriminating amplifier 12 includes anysuitable amplifier circuitwhich has the characteristics of a singlechannel dififerentialdiscriminator, as described in Elec- Homes-Experimental Techniques, byW. C. Elmore'and M.- Sands,=McGraW-Hill (1949), p. 228, tl. All countsare'amplified and one amplified pulse is emitted through conductor 13for each radioactive impulse detected by the probe It and falling withinthe selected pulse height range. a

A rate meter 15 is connected to the conductor 13. The rate meter 15 isof the usual type which will indicate the count rate being detected. Arange control 16 is provided for selecting an appropriate scale on meterdial 17. A time constant selector 18 is provided. The time 3 constant isa length of time over which the count rate is measured to determine the.rate. The longer the time constant, the more stable will be the readingon the dial 17. Preferably, a time constantrange of from one-eighth tofive seconds. is provided. Whenthe device is in operation, any change inthe count rate will be reflected by the output of the. ratemeter, butthat reflection will lag by a length of time proportional to the timeconstant. A rate. meter of the type described is currently sold byPicker X-Ray Corp.,,Waite ManufacturingDivision, Inc., as Cat. 2805.

The output of the-rate meter 15 is conducted by a conductor 19 to a.variable gain, direct, coupled. amplifier 20. The. output of the, ratemeterin the preferred and disclosed arrangement is between and 7 voltsDC at all times. With a selected study it may be known, for example,that the count rate will vary between 6 and 8 thousand. counts perminute. The 10,000 count per minute scale on the rate meter will beselected and it will therefore be known. that the output voltage of therate meter will vary between 60 and 80 percent of the maximum 7 volts.With this example the output voltage will vary from 4.2 to 5.6. volts.This provides a voltage difference of 1.4 volts. With this example thevariable amplifier 20 is adjusted. sov that it varies from minimum tomaximum output with an input variation of 1.4 volts. Thus, in thisexample, the amplifier output will be at a minimal voltage; when theinput to the amplifier is 4.2 volts and at a maximum voltage; when theinput is 5.6 volts.

A power supply 21 is provided which. preferably has an output of from500m 900 volts. A conductor 22 connects the variable amplifier 20 to thepower supply 21. The varying output of the variable amplifier controlsthe power supply and causes its output to vary proportionally with thevariable amplifier output and therefore with the probe count rate. inFIGURE 2, which will be described presently. Another is the type shown;at page 365v of Electronics- Experimental Techniques, while stillanother is'that sold by Picker X-Ray Corp., Waite ManufacturingDivision, Inc., as Cat. 2813.

The output of the power supply 21 is'connected through a conductor 24 toan accelerating electrode 23-. The accelerating electrode or ring formsa part of a cathode ray tube shown generally at 25. One suitablecathoderay tube is RCA type C73687A.

A one shot multivibrator 26 is also connected to the conductor 13. Themultivibrator is of the type which will emit one impulse of apredetermined. time duration and power for each pulse transmitted to it:by the conductor 13. Preferably, the one shot multivibrator includes anadjustment tovary the time. duration of the emitted pulses. The timeduration may, forexample, be from 1 to 100 microseconds. vibrator isdisclosed at pages 88 through 91' of Electronics-ExperimentalTechniques.

The one shot multivibrator 26 is connected through conductor 27 tocathode 28 of the cathode ray tube 25. A coupling condenser 29 isincluded in-the conductor 27 The cathode 28 is grounded through abiasing resistor 30.

The cathode ray tube 25 includes a control grid 32 and an acceleratingor'focusing anode 33. The control grid 32 is connected to ground througha conductor 34. The focusing or accelerating an0de-33'has its voltagesupplied by a voltage divider- 35 and 36 which is connected across thepower supply 21.

The cathode ray tube 25 includes the-usual target 37' inthe formv ofafluorescent screen. A collimator 38- focuses the emitted light to anappropriate sized dot forimpingement on a: photographic film 40.

Circuitry for asuitable variable gain amplifier 20- and' for a suitablepower supply 2 1' is shown in FIGURE 2. The conductor 19 connects therate meter 15 to a resistor 45. A: pluralityof contacts 46are providedat spaced One suitable power supply is shown.

A suitable one shot multilocations along the resistor. A moveablecontact 47 is connectable to a selected one of the contacts 46.

The appropriate one of the contacts 46 is selected by determining whatpercentage of the selected rate meter scale is represented by thedifference between maximum and minimum count rate readings. If thispercentage is, for example, percent, the moveable contact 47 is engagedwith the contact 46 which will place 20 percent of the resistor betweenthe moveable contact 47 and the rate meter 15. With an appropriatesetting, the maximum voltage change in the conductor 48 in any study isequal to the maximum change in any other study in which proper settingsare made.

The conductor 48' energizes grid 49 of a triode 50. Anode 52 of thetriode 50 is connected to the conductor 22. The conductor 22 conductsthe output of the triode 50 to the power supply. The anode 52 isenergized by a positive voltage supply at 53. Cathode 54 of the triode50 is connected to ground through a potentiometer 55.

When the probe is placed over an area of maximum activity and the ratemeter registers the maximum count rate, the output of the power supplyis adjusted by varying the potentiometer 55. The conductor is connectedto grid 56 0f power supply control tube 57. Thus, the output of thepower supply is controlledby varying the input to the grid 56 of thecontrol tube 57.

The output of the control tube 57 is connected to grid 60' of the usualseries connected power regulating triode 61. Thus, adjustment of thepotentiometer 55 varies the output of the power regulating tube 61 andthat output is registered on voltmeter 62.

With the described mechanism it will be seen that once the discriminatedlevel of activity is obtained one light impulse will be emitted by thecathode ray tube 25 for each count detected by the probe and passed bythe amplifier 12. The intensity of the emitted light pulse will varywith the count rate because the voltage on the focusing anode varieswith the count rate. Thus, the intensity, or density, of an exposure onthe film 40 in any given spot will reflect the count rate in acorresponding spot in the area studied. Since the probe and the cathoderay tube move together as a scan is conducted, the resultant filmexposure is a graphic reproduction which outlines the distributionpattern and the concentration of radioactivity'in an area under study.

Method of Operation The method of operation of the device can best beunderstood if a specific example is employed in the description. Thestudy of a human liver is an excellent example. In such a studyaquantity of radioactive colloidal gold or other suitable radioactivesubstance is first administered intravenously. After an interval ofabout ten minutes the patient is positioned on a stretcher or othersupport beneath the probe. The probe is directed toward the approximatearea of the liver.

Afterthe probe is positioned, the rate meter time constant is setat itslowest level, A; of a second in the disclosed arrangement. An audiblesound producer, which is preferably supplied, is turned on. Next, theprobe is shifted until the center of'highest radioactive concentrationis determined. The pitch of the audible sound and/ or the indications ofthe rate meter may be used for 10- cating this point of highestconcentration. Once the point of maximal radioactivity has beendetermined, the indicated count on the rate meter is observed. To obtaina dependable average count-per-minute rate over a relatively long periodof time, it is good practice to then adjustthe time constant toarelatively high value such as 5 seconds and adjustthe meter range topermit the maximum sensitivity within the capacity of the meter. Bymaximum sensitivity itis meant, for example, if the count-per-minutemaximum is under 10,000; the 10,000 scale would be used. If it is inexcess of 10,000, then one must use the next highest scale, for example,a 30,000 count per minute scale.

After the maximal count-per-minute rate has been determined, the minimalaverage count-per-minute rate should be determined in a similar fashionby, for example, moving the probe over the upper chest or lower abdomen.Having detenmined these two rates a percentage of 100% of the capacityof the selected rate scale is determined tor both maximum and minimumrates. The difference between the maximum and minimum percentages is thecount-per-minute range differential. The movable contact 4-7 of thevariable amplifier is then set according to that range differential.

Next, the probe is positioned for the maximum count rate. Thepotentiometer 55 is then adjusted until the voltmeter d2 registers thedesired maximum power supply output voltage. In the specific examplegiven this desired maximum is 900 volts.

An appropriate time duration for the pulses emitted by the one shotmultivibtator is selected and the one shot multivibrator isappropriately adjusted. This may be reterred to as an adjustment in thedensity, since it affects the density of the photographic image whichwill be obrained. Once these described adjustments have been made thestudy may be undertaken.

While the invention has been described with a great deal of detail it isbelieved that it essentially comprises a scintillation photorecordingmechanism including a scintillation probe, a cathode ray tube, meansconnecting the output of the probe to the cathode anda power supplyconnected to the cathode ray tube accelerator with a power supplycontrol means varying the voltage of the power supply in accordance withthe count rate detected by the probe.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by Way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to Withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

In the claims: I p

1. In a scintillation recording mechanism the improvement comprises, ascintillation probe, a cathode ray tube having an electron emittingcathode and electron acceleration means, means connecting the probe tothe cathode, a power supply connected .to the acceleration means, andpower supplycontrol means connected to the probe and to the power supplyto vary the power supplied to the acceleration means in proportion tothe frequency of impulses emitted by the probe;

2. The device of claim 1 wherein the tube includes a grounded controlgrid.

3. In a scintillation recording mechanism the improvement comprises, ascintillation probe, a cathode ray tube having an electron emittingcathode and electron acceleration means, adjustable pulse emitting meansfor emitting one pulse of a predetermined and selected time duration foreach signal pulse received, conductor means connecting the probe to thepulse emitting means to transmit signals from the probe to the pulseemitting means and connecting the pulse emitting means to said cathodeto transmit emitted pulses from the pulse emitting means to the cathode,a power supply connected to the acceleration means, and power supplycontrol means connected to the probe and to the power supply to vary thepower supplied to the acceleration means in proportion to the frequencyof impulses emitted by the probe.

4. In a scintillation recording mechanism the improvement comprises, ascintillation probe, a cathode ray tube having an electron emittingcathode and electron acceleration means, a discriminating amplifierconnected to .the probe, means connecting the amplifier to the cathode,a power supply connected to the accelerator means, and

3 power supply control means connected to the amplifier and to the powersupply to vary the voltage supplied to the accelerator means inproportion to the impulses emitted by the probe. 7

5 The device of claim 1 wherein said power supply controlmeans'comprisesa rate meter and a variable gain amplifier.

6. The device of claim 1 wherein said tube has a grounded control gridand a focusing anode and wherein the focusing anode is connected to saidpower supply through a resistor.

7. A device for emitting signals suitable for measuring and graphicallyrecording the distribution of a radioactive substance comprising, ascintillation probe, a discriminating amplifier electrically connectedto the probe, a rate meter electrically connected to the discriminatingamplifier and including means to adjust the output level to produceoutput voltages proportional to the activity measured by the probe andwithin apredetermined output voltage range, a variable amplifierelectrically connected to the rate meter to produce an output voltageproportional to the rate meter output, a high voltage power supplyelectrically connected to the variable amplifier and responsive to theoutput of the latter, a cathode ray tube having an electron emittingcathode and an electron accelerating member, the accelerating memberbeing connected to the power supply, a one shot multivibra-tor includingmeans to adjust the duration of an output pulse, and said multivibratorbeing connected to the discriminating amplifier and to said cathode.

8. The device of claim 7 wherein the cathode ray tube has a control gridand wherein the control grid is grounded.

9. The device of claim 1 wherein said means connecting the probe to thecathode includes a multivibrator having means to adjust the duration ofan output pulse.

10. The device of claim 4 wherein said means con-.

necting the amplifier to the cathode includes a multivibrator havingmeans to adjust the duration of an output pulse. 1

11'. The device of claim 1 wherein the power supply control meansincludes a rate meter having independent means to control the range andto control the time constant.

12. The device of claim 4 wherein the power supply control meansincludes a rate meter having independent means to control the range andto control the time constant.

13. The device of claim,7 wherein the means included in the rate meterto adjust the output level includes independent means to control therange and to control the time constant. j

' 14. A device for emitting signals for use by a photo recordingmechanism comprising, a probe for emitting impulses in response toradioactivity detected, a discriminating amplifier connected to theprobe for emitting impulses when the activity detected by the probe isabove a predetermined minimum level; a light emitting tube having acathode, an anode, and a means to control the brightness of an imageproduced on the anode; means connecting the discriminating amplifier tothe tube cathode, other means connecting the discriminating amplifierto'the brightness control means, and said other means including a ratemeterhaving presettable means to independently adjust both the range andtime constant prior to'the conduction of a study and thereby utilize thefull range of the brightness eontrol means between said predeterminedminimum level of activity and the maximum activity encountered during agiven study.

15. The device of claim 14 wherein the means connecting the amplifier tothe cathode includes a one shot multivibrator which emits one pulse of apredetermined duration and power for each impulse received.

16. The device of claim 15 wherein the time duration of themultivibrator pulse is presettable to obtain an adjustable predeterminedpulse duration.

17. In a scintillation recording mechanism the improvement whichcomprises a scintillation probe to give signal pulses at a rateproportional to radioactivity detected, an electronic device having anenergy emitting electrode and energy acceleration means; meansconnecting the probe to the energy emitting electrode, said electrodeemitting an energy pulse for each signal pulse received from thescintillation probe, a power supply connected to the acceleration means,and power supply control means connected to the scintillation probe andto the power supply to vary the power supplied to the acceleration meansin proportion to the frequency of signal pulses emitted by thescintillation probe so that energy pulses emitted by said electrode areincreased in intensity by the acceleration means as the frequency ofsignal pulses emitted by the scintillation probe increases.

18. The device of claim 17 wherein the power supply control meansincludes a rate meter and a variable amplifier, said rate meter beingconnected to the scintillation probe and producing an output controlvoltage which varies in proportion to changes in the frequency of thesignal pulses, said variable amplifier connected between said rate meterand said power supply and matching the maximum and minimum points of theoutput control voltage to maximum and minimum voltage pointsrespectively of the power supply so that the maximum and minimumintensity of the energy pulses emitted by said electrode as controlledby the acceleration means corresponds precisely to the maximum andminimum points respectively of the rate meter output control voltage.

19. The device of claim 17 wherein a one-shot multivibrator is connectedbetween said scintillation probe and said energy emitting electrode andproduces an electrical pulse for each signal pulse received from saidscintillation probe, said one shot multivibrator having means to adjustthe duration of said electrical pulse.

20. The device of claim 17 wherein a discriminating amplifier isconnected to said scintillation probe and passes only those signalpulses which are between a predetermined range of amplitudes.

21. The device of claim 20 wherein the power supply control meansincludes a rate meter and a variable amplifier, said rate meter beingconnected to the discriminating amplifier and producing and outputcontrol voltage which varies in proportion to changes in the frequencyof the signal pulses, said variable amplifier connected between saidrate meter and said power supply and matching the maximum and minimumpoints of the output control voltage to the maximum and minimum voltagepoints respectively of the power supply so that the maximum and minimumintensity of the energy pulses emitted by said electrode as controlledby the acceleration means corresponds precisely to the maximum andminimum points respectively of the rate meter output control voltage.

22. The device of claim 21 wherein a one-shot multivibrator is connectedbetween said discriminating amplifier and said energy emitting electrodeand produces an electrical pulse for each signal pulse received fromsaid discriminating amplifier, said one shot multivibrator having meansto adjust the duration of said electrical pulse.

23. In a scintillation recording mechanism the improvement comprising:

(a) a scintillation responsive means to give signal pulses at a rateproportional to radioactivity detected;

(b) an electronic device having an electron emitting means and anelectron acceleration means;

(c) means energizing said electron emitting means;

(d) a power supply connected to the acceleration means; and

(6) power supply control means connected to the scintillation responsivemeans and to the power supply to vary the power supplied to theacceleration means 8 in proportion to the frequency of the pulsesemitted I by said scintillation responsive means.

24. The combination of claim 23 wherein said electronic device is acathode ray tube.

25. The combination of claim 23 wherein the power supply control meansincludes a ratemeter producing an output control voltage proportional tothe frequency of the pulses emitted by the scintillation responsivemeans and having means to adjust the level of the output voltage 10within a predetermined voltage range.

26. The combination of claim 23 wherein the power supply control meansincludes a ratemeter producing an output control voltage proportional tothe frequency of the pulses emitted by the scintillation responsivemeans and having means to adjust its voltage range and its timeconstant.

27. In a scintillation recording mechanism the improvement comprising:

(a) a scintillation probe having an output for producing signal pulsesat a rate proportional to radio activity detected;

(b) a discriminating amplifier having an input connected to the outputof the scintillation probe and an output for producing signal pulsesbetween a predetermine range of amplitudes;

(c) a ratemeter having an input connected to the output of thediscriminating amplifier and an output for producing an output controlvoltage which varies in proportion to the frequency of the signal pulsesapplied to its input;

(d) an electronic device having an electron emitting electrode and anelectron acceleration means;

(e) means energizing said electron emitting electrode to cause theemission of electrons;

(f) a power supply connected to the acceleration means; and

(g) means connecting the output of said ratemeter to said power supplyso that the power supplied to said acceleration means varies inproportion to the output control voltage of the ratemeter.

28. In a scintillation recording mechanism the improvement comprising:

(a) a scintillation probe to give signal pulses at a rate proportionalto radioactivity detected; 5 (b) an electronic device having an electronemitting electrode and an electron acceleration means;

(c) means energizing said electron emitting electrode to cause theemission of electrons;

(d) a ratemeter connected to the scintillation probe and producing anoutput control voltage which varies in proportion to the frequency ofthe signal pulses;

(e) a power supply connected to the acceleration means; and,

(f) a variable amplifier connected between said ratemeter and said powersupply and matching the maximum and minimum points of the output controlvoltage to the maximum and minimum points respectively of the powersupply so that the maximum and minimum intensity of the electronemission by said electron emitting electrode as controlled by theacceleration means corresponds to the maximum and minimum pointsrespectively of the ratemeter output control voltage.

29. In a scintillation recording mechanism, the improvement whichcomprises:

(a) a scintillation detection means to provide signal pulses at a rateproportional to radioactivity detected;

(b) a light source;

(0) circuit means connecting the light source to the scintillation meansto cause said light source to produce a light pulse after receiving apredetermined number of signal pulses from the scintillation means; and,

(d) control means connected to the scintillation detection means and tothe light source to vary the in- 9 tensity of light pulses emitted bythe light source in proportion to the frequency of signal pulses emittedby the scintillation means whereby the light pulses emitted by the lightsource vary in intensity and in frequency as the frequency of the signalpulses emitted by the scintillation means varies.

References Cited by the Examiner UNITED STATES PATENTS 2,769,094 10/56Linlor 25071.5 2,922,885 1/60 Tittle 25071.5

19 OTHER REFERENCES Simple Recording Gamma-Ray Spectrometer, by W. H.Venable, Jr., from Nucleonics, vol. 15, No. 7, July 1957, pp. 84, 85 and86.

Techniques for the Visulization of Internal Organs by an AutomaticRadioistope Scanning System, by W. J. Maclntyre et al., fromInternational Journal of Applied Radiation and Isotopes, 1958, vol. 3,pp. 193 to 206, published by Pergamon Press Ltd., London, England.

RALPH G. NILSON, Primary Examiner. ARCHIE R. BORCHELT, Examiner.

3. IN A SCINTILLATION RECORDING MECHANISM THE IMPROVEMENT COMPRISES, ASCINTILLATION PROBE, A CATHODE RAY TUBE HAVING AN ELECTRON EMITTINGCATHODE AND ELECTRON ACCELERATION MEANS, ADJUSTABLE PULSE EMITTING MEANSFOR EMITTING ONE PULSE OF A PREDETERMINED AND SELECTED TIME DURATION FOREACH SIGNAL PULSE RECEIVED, CONDUCTOR MEANS CONNECTING THE PROBE TO THEPULSE EMITTING MEANS TO TRANSMIT SIGNALS FROM THE PROBE TO THE PULSEEMITTING MEANS AND CONNECTING THE PULSE EMITTING MEANS TO SAID CATHODETO TRANSMIT EMITTED PULSES FROM THE PULSE EMITTING MEANS TO THE CATHODE,A POWER SUPPLY CONNECTED TO THE ACCELERATION MEANS, AND POWER SUPPLYCONTROL MEANS CONNECTED TO THE PROBE AND TO THE POWER SUPPLY TO VARY THEPOWER SUPPLIED TO THE ACCELERATION MEANS IN PROPORTION TO THE FREQUENCYOF IMPULSES EMITTED BY THE PROBE.